Rotary coin mechanisms are used widely for such devices as vending machines and the like. A typical example is a so-called "bulk vendor", colloquially known as a "gumball machine", which stores product in a product storage bin and dispenses the product upon rotation of the coin mechanism. One of many examples of such a bulk vendor is described in U.S. Pat. No. 5,383,545 to Schwarzli issued Jan. 24, 1995 for a "Coin Mechanism", which is incorporated herein by reference.
Bulk vendors are designed for self service by users with minimal maintenance, and as such are frequently placed in locations where their use cannot readily supervised. As a result bulk vendors are constantly subjected to attempts to steal merchandise.
The most common type of theft from bulk vendors involves the use of "slugs", which are usually disc-shaped pieces of metal, and more recently plastic and dense cardboard, approximating the size and configuration of the coin or token which the coin mechanism is designed to accept. Slugs composed of plastic or sturdy cardboard have recently become popular due to their low cost and the ease with which such slugs can be produced to the required size. This has led to the development of measuring devices with fairly precise tolerances, capable of determining the thickness and diameter of the inserted coin to within a few thousandths of an inch.
However, cardboard slugs in particular present a problem in bulk vendors, despite the precision of the measuring devices, because of the manner in which a conventional rotary coin mechanism discriminates between coins or tokens of the intended configuration and other coins, tokens or slugs. In a typical rotary coin mechanism a coin recess is provided in a rotating coin conveyor disc, and a pair of dogs respectively measure the thickness and diameter of the inserted coin or slug as the rotational cycle begins. Either dog will arrest rotation of the mechanism if the diameter or thickness does not match that of the intended denomination of coin. Such measuring devices are described in the aforementioned U.S. Pat. No. 5,383,545, and are generally effective in preventing rotation of the mechanism when a slug or incorrect denomination of coin is inserted.
However, in the case of slightly oversized cardboard slugs of the correct thickness, repeated attempts to force the mechanism to turn with the slug in the coin recess will result in gradual paring away of the edge of the slug by the perimeter measuring dog itself, and once the edge has worn to a point within the tolerance of the measuring dog, the mechanism will accept the slug. This "self-sizing" of cardboard slugs has become a significant problem resulting in extensive losses to bulk vendor operators.
It is known to provide a coin mechanism with ridges or ribs in the coin slot, which are adapted to allow only compatibly grooved tokens to be inserted into the coin recess. However, these suffer from the disadvantage that compatible grooves can often be easily filed into the face of a slug of the appropriate size. Moreover, in the case of cardboard and plastic slugs, which are somewhat flexible, the slug can be bent around the ribs in the coin slot which are intended to prevent the insertion of a coin or token that is not equipped with suitable grooves. In both cases the security offered by the ridges or ribs is defeated.